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The Protein Crystal Growth - Single Thermal Locker System (PCG-STES) has been designed to crystallize macromolecules in microgravity.

The PCG-STES is very autonomous, minimal crew time is required for activation, deactivation and periodic status checks of the hardware.

Description

The Protein Crystal Growth - Single-Locker Thermal Enclosure System (PCG-STES) provides a controlled-temperature environment between 1 and 40 degrees C to grow large, high-quality crystals. Its thermal control system (TCS) regulates the temperature inside the payload chamber. A fan pulls cabin air through an intake on the front panel causing the air to flow across the heat exchanger fans, and then out the rear left side of the unit. Push buttons and an LCD display on the front panel allow the crew to command the unit. STES can also be commanded from the ground.

Samples were housed in the PCG-STES and within two different types of crystallization hardware: the Protein Crystallization Apparatus for Microgravity (PCAM) or the Diffusion-Controlled Crystallization Apparatus for Microgravity (DCAM).

PCAMs consist of nine trays, each containing seven vapor-equilibration wells. The nine trays are sealed inside a cylinder. Crystals are formed by the "sitting drop" method of vapor diffusion. Each sample well holds a drop of protein solution and precipitant (salts or organic solvents, which draw water away from the protein solution) mixed together. A surrounding moat holds a reservoir, filled with an absorbent fluid, that draws moisture away from the mixed solution. Crystals form as the moisture is absorbed. A rubber seal pressed into the lip of the reservoir keeps crystals from forming on Earth or from bouncing out of their wells during transport. Each cylinder holds 63 experiments for a total of 378 experiments inside the Single-locker Thermal Enclosure System (STES).

DCAMs, which are slightly smaller than a 35-mm film canister, each contained two cylindrical chambers that are connected by a tunnel. One chamber holds the precipitant solution and the other contains the protein sample. A thin semipermeable membrane covers the protein sample that allowed the precipitant to pass through at a controlled rate. The rate of diffusion was controlled by a porous plug that separates the two chambers. This is referred to as the liquid-liquid diffusion method.

Crewmembers transferred the experiment hardware, PCG-STES (containing the DCAM and PCAM chambers with the experiment samples) from the Space Shuttle Middeck to the ISS EXPRESS Rack. The experiment was activated on Earth where the sample and precipitant were added to their chambers.

The PCG-STES hardware has supported nine experiments onboard the ISS, with additional shared samples for associated investigators. Samples were taken to and from station five times for crystallization during Expeditions 2, 4, 5, and 6. PCG-STES samples in DCAM were on orbit prior to the space shuttle Columbia accident, and then spent an unprecedented 981 days (November 2002 - August 2005) on ISS before being returned on STS-114/LF1(Kundrot 2002).

Information provided by the investigation team to the ISS Program Scientist's Office. If updates are needed to the summary please contact JSC-ISS-Program-Science-Group. For other general questions regarding space station research and technology, please feel free to call our help line at 281-244-6187 or e-mail at JSC-ISS-Payloads-Helpline.